The invention is in the field of light units, such as screw-in circular fluorescent lights, and light units having selectable light levels such as bright and dim, or variable dimming.
Three-way incandescent light bulbs have been popular for many years, for use in situations where differing light levels are desirable under differing conditions, and to conserve electrical power consumption by adjusting the light level to the lowest value suitable for the needed visual task. Fluorescent lamp units are more electrically efficient than incandescent lamps, and ways have been proposed for providing multiple-light level fluorescent lamp units. For example, U.S. Pat. Nos. 2,350,462 to Johns, 2,652,483 to Laidig, and 4,178,535 to Miller, disclose ways of providing selectably different light levels for circular fluorescent lights by inserting different reactive ballast elements, or different transformer winding turns, in series with the lamp bulbs. The general idea of a screw-in ballasted fluorescent lamp unit has been known, for example, by the disclosure in U.S. Pat. Nos. 2,320,424 to Gates and 2,817,004 to Baumgartner. U.S. Pat. Nos. 3,249,807 to Nuckolls and 3,500,124 to Babcock disclose variable brightness lamp devices having phase-controlled switching circuits.